Re: PWM Controller question - SSTC Modulation

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Original poster: "Eastern Voltage Research Corporation" <dhmccauley-at-easternvoltageresearch-dot-com> 

I have explored this although haven't built anything.

The problem with the ISSTC is that it would require you to run CW (although
the rails would be AM modulated) and its very
doubtful the IGBTs would be able to handle that type of power without some
really serious cooling.  Remember, in ISSTC mode,
we are only running maybe 10% duty cycle tops.

Also, i don't think you would see the big 10 foot arcs with that type of
high-side modulation (non-interrupted) arrangement.
You would still probably get the pretty big brush like discharge with
occasional peaking.

HOWEVER! ! ! ! !

I had an idea of using the ISSTC to audio modulate with the full length of
arcs and ULTIMATE BASS RESPONSE.
Basically, this entails interrupting the ISSTC at the audio frequency of the
tone you wish desired.  I am already working on
a design for this and it will interface to a two octave keyboard.  You press
a key, and the ISSTC arcs to the audio frequency of
the key you press.

I think Alan Sharpe used this type of simple audio modulation in his quad
SSTC last year, although his was PIC controlled to play
close encounters theme or something.

Dan


 > I have this crazy idea that bigger sparks will give better bass response,
 > so I would love to see Steve Ward give his interrupter a rest, turn down
 > the rail voltage half way, and high side modulate that sucker! People say
 > it can't be done, but it is done with 50, 60, 100, and 120 Hz all the
time.
 > Finding a suitable mod transformer that can handle that much current, and
 > has the correct impedance match would be challanging, and maybe even
 > impossible though. Someone once suggested substituting the mod transformer
 > with an SCR or something. If someone could come up with a way of high side
 > modulation with active power devices in place of a modulation transformer
 > it would be great! Even if he settled with driver side modulation, I would
 > love to see what kind of audio comes out of a 10 foot arc! The nice thing
 > about high side, high fidelity modulation is that throbbing base will
 > produce long streamers if you are fully modulating (ie: the rail voltage
 > will peak at double the! supply voltage with no modulation, and then dip
to
 > 0 volts during an audio cycle).
 > Sue